Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$46.73	13.856%	$53.2049	$53.20	$53.20	$53.20
Purchase #2	$174.35	4.624%	$182.4119	$182.41	$182.40	$182.40
Purchase #3	$195.69	9.553%	$214.3843	$214.38	$214.40	$214.40
Purchase #4	$131.69	7.510%	$141.5799	$141.58	$141.60	$141.60
Purchase #5	$36.54	6.749%	$39.0061	$39.01	$39.00	$39.00
Purchase #6	$87.43	11.843%	$97.7843	$97.78	$97.80	$97.80
Purchase #7	$100.41	11.371%	$111.8276	$111.83	$111.85	$111.80
7 purchase totals =	$772.84		$840.1990	$840.19	$840.25	$840.20